Metronomes have been around for almost 200 years. The first metronomes were mechanical with a baton that swung back and forth and produced a click. Purely mechanical (non-electrical) metronomes tend to be expensive and capricious. Clockworks are difficult to produce and can easily age and deteriorate. Mechanical metronomes also require periodic winding which can be a distraction and an annoyance. The problems with mechanical metronomes led to the more recent development of electronic metronomes.
Electronic metronomes use electricity to drive a motor to swing the baton instead of clock works, or they produce a tone or light to indicate the beat. The only improvement the electromechanical metronomes offer over the older types is an end to winding and an increase in accuracy. Purely electronic metronomes also have their detractions. Blinking lights are a distraction when attempting to play an instrument and are not especially useful for keeping time. The tone produced is often loud and piercing. This makes them aggravating to the musician.
All metronomes (electrical or mechanical) that produce noise have a limitation: since music is an audible medium, the noise made by the metronome intrudes upon and diminishes the enjoyment of the music being played. Sound-producing metronomes detract from the very thing they are meant to enhance. Neither musician nor a possible audience can fully enjoy the music because of the external, non-musical noise.